Material application systems are used to apply one or more powder coating materials to an object. General examples are powder coating systems and other particulate material application systems such as may be used in the food processing and chemical industries. These are but a few examples of wide and numerous varieties of systems used to apply particulate materials to an object.
There are two generally known types of dry particulate material transfer processes, referred to herein as dilute phase and dense phase. Dilute phase systems utilize a substantial quantity of air to push material through one or more hoses or other conduit from a supply to a spray applicator. A common pump design used in powder coating systems is a venturi pump which introduces a large volume of air under pressure and higher velocity into the powder flow. In order to achieve adequate powder flow rates (in pounds per minute or pounds per hour for example), the components that make up the flow path must be large enough to accommodate the flow with such high air to material (in other words lean flow) otherwise significant back pressure and other deleterious effects can occur.
Dense phase systems on the other hand are characterized by a high material to air ratio (in other words a “rich” flow). A dense phase pump is described in U.S. patent application Ser. No. 10/501,693 filed on Jul. 16, 2004, and issued as U.S. Pat. No. 7,150,585, entitled PROCESS AND EQUIPMENT FOR THE CONVEYANCE OF POWDERED MATERIAL, the entire disclosure of which is appended hereto and fully incorporated herein by reference, and which is owned by the assignee of the present inventions. This pump is characterized in general by a pump chamber that is partially defined by a gas permeable member. Material, such as powder coating material as an example, is drawn into the chamber at one end by gravity and/or negative pressure and is pushed out of the chamber through an opposite end by positive air pressure. This pump design is very effective for transferring material, in part due to the novel arrangement of a gas permeable member forming part of the pump chamber. The overall pump, however, in some cases may be less than optimal for purging, cleaning, color change, maintenance and material flow rate control. A useful feature of this pump is that it can be operated in reverse and forward modes for purge operations.